1. Field of the Invention
The present invention relates to a fluorescent transilluminator for exposing an object to be irradiated to ultraviolet rays to make it fluoresce.
2. Description of the Related Art
It has been known that a DNA analysis system uses gel electrophoresis as one of the remarkably effective techniques for analyzing nucleic acids or proteins. In the gel electrophoresis, an electric field is applied to a gel containing an electrolyte. Then, charged particles move in the gel. In this event, differences among the charged particles in size, shape, charge, and so on cause differences among respective moving rates of charged particles. Using the differences among the moving rates allows separating molecules of the nucleic acids, the proteins, or the like.
The nucleic acids separated by electrophoresis as described above are not visible, when they are left as they are, so, in order to observe the nucleic acid separated, the gel is stained with a solution of fluorescent substance (e.g., ethidium bromide) bindable to the nucleic acid. In some instances, a fluorescent substance such as ethidium bromide is previously added in preparing the gel. If the gel stained with fluorescent substance in this way is exposed to ultraviolet rays, portions corresponding to the nucleic acid fluoresce in orange. This allows observation of the nucleic acids. In this event, subjecting a marker, of which the molecular weight has been known, to electrophoresis together with a sample allows measurement of the molecular weight of the sample.
An ultraviolet lamp unit used for irradiating ultraviolet rays as described above is collectively named xe2x80x9cfluorescent transilluminatorxe2x80x9d.
In such an analysis, while the analysis is so far generally carried out on a photograph of fluorescing gel taken with a Polaroid camera, it is the recent method that the analysis is carried out with a computer on a series of images taken with a CCD camera, projected on a monitor, and recorded. In the latter case, since the analysis is carried out by measuring fluorescence strength, the recorded data is required to be precise.
For example, such a technique as described above is disclosed in Japanese Published Unexamined Patent Application No. 1993-215714,that the electrophoretically treated gel, of which internal molecule has been separated by gel electrophoresis, is mounted on an ultraviolet irradiation apparatus containing the ultraviolet lamp and is caused to fluoresce, and then the analysis of fluorescence is carried out using the computer. The ultraviolet irradiation apparatus disclosed in the publication has, as shown in FIG. 1, a structure in which a top surface of case 1 containing ultraviolet lamp 2 is covered with ultraviolet rays permeable glass 3. Electrophoretically treated gel 4 is exposed to ultraviolet rays, being mounted on the ultraviolet rays permeable glass 3.
A fluorescent transilluminator similar to this has been also disclosed in U.S. Pat. No. 5,347,342 and others. In the fluorescent transilluminator disclosed in the application, a top window (opening) is formed on the case containing an ultraviolet source. The top window has a structure in which a visible light-cutting filter (ultraviolet band filter) is installed and the sample is put above the visible light-cutting filter. Through this structure, ultraviolet rays emitted from the ultraviolet source are transmitted through the top window having the visible light-cutting filter and irradiated to the sample.
Generally, xe2x80x9cultraviolet rays (UV)xe2x80x9d are the generic name of electromagnetic waves with wavelengths ranging from about 10 nm to 380 nm and is divided into the following 3 classes.
The first class comprises ultraviolet rays with wavelengths ranging from about 315 nm to 400 nm, which are called UV-A and also called near ultraviolet rays. These near ultraviolet rays have a pigmentation (so-called sunburn) function.
The second one comprises ultraviolet rays with wavelengths ranging from about 280 nm to 315 nm, which are called UV-B. The ultraviolet rays with these wavelengths cause erythema (irritating the skin). It is also said that this ultraviolet rays are necessary for biosynthesis of vitamin D.
The third one comprises ultraviolet rays with wavelengths ranging from 100 nm to 280 nm, which are called UV-C. This ultraviolet rays also called disinfecting rays have a literally disinfecting function.
For the fluorescent transilluminator, since ultraviolet rays in the UV-B band can effectively make a fluorescent substance (ethidium bromide) fluoresce, the light source that emits ultraviolet rays of the UV-B band is adopted. For the light source of such a fluorescent transilluminator as currently available in the market, a mercury fluorescent lamp, which is assembled with a fluorescent body such as ((Ca, Zn)3(PO4)2:Tl) having an emission peak within a UV-B wavelength band ranging from about 280 to 315 nm, is used.
As described above, the light source of the fluorescent transilluminator used currently is a mercury-based light source lamp, in which mercury is sealed, such as an ultraviolet fluorescent lamp or a mercury lamp having a mercury line spectrum as its excitation source. In such a mercury-based light source lamp, when it is used in a low temperature atmosphere, the mercury vapor pressure reduces and the start of discharge becomes difficult. Moreover, after discharge is started, vapor pressure of sealed mercury rises in accordance with temperature increase after lighting of the lamp, emission strength thereby varies from immediately after the lamp is started until a condition becomes stable, and thus a long time is required to stabilize the light output. In this way, the mercury-based light source lamp conventionally used has a disadvantage of requiring a long start-up time particularly in cold districts and in the winter season. In addition, in the case where the mercury fluorescent lamp is used for an analysis of nucleic acids and proteins such as the abovementioned, because of the long required time to stabilize the light output and start the analysis, the problem may arise that before start of the analysis, a sample, particularly a delicate sample such as a DNA sample, is damaged.
Moreover, light emitted from the conventional mercury fluorescent lamp contains visible light components and hence, in the case where such a mercury fluorescent lamp is used as the light source, in order to assure that the visible light components do not adversely affect an observation, it becomes essential to use the visible light-cutting filter for transmitting ultraviolet rays and cutting the visible light. However, this filter is a peculiar filter and very expensive due to its specialty so that it costs 30 to 80 percent of the commercial price of a fluorescent transilluminator product.
Further, the mercury fluorescent lamp as the conventional light source of the fluorescent transilluminator provides such a weak emission strength that it may not make the sample for observation fluoresce sufficiently.
Therefore, it is an object of the present invention to provide a fluorescent transilluminator requiring no visible light-cutting filter. In addition, it is another object of the present invention to provide the fluorescent transilluminator, which is excellent in the start-up characteristic even in a low temperature atmosphere and can emit ultraviolet rays of strong intensity for making a sample fluoresce sufficiently.
With a purpose to achieve the above described objects, the fluorescent transilluminator according to the present invention has a light source emitting only ultraviolet rays with a sharp emission spectrum, particularly, the emission spectrum having a peak emission wavelength at 313 nm with 5 nm or shorter half width. Therefore, the fluorescent transilluminator according to the present invention can be adapted to irradiate an object with ultraviolet rays emitted by the ultraviolet source without cutting of visible light but only through a space and/or a member transmitting light having wave lengths equal to or longer than 300 nm, ranging from the ultraviolet region to the visible light region and this allows the transilluminator to assure that no disturbance occurs in the observation such as in gel electrophoresis. Consequently, a costly visible light-cutting filter is no longer required.
The ultraviolet source, which can emit such a sharp emission spectrum, can be formed by using a gadolinium-activated fluorescent body. Wherein, for an excitation source for exciting the fluorescent body to make it fluoresce, using xenon discharge is advantageously used. Utilization of such an excitation source using xenon discharge allows the ultraviolet source to be of an excellent start-up characteristic almost suffering no influence of an ambient temperature in contrast to the conventional mercury fluorescent lamp. Moreover, the ultraviolet source can emit an emission of stronger intensity than that of the conventional mercury fluorescent lamp.
In the fluorescent transilluminator according to the present invention, a transmission window formed of a glass plate can be installed, which can transmit light with wavelengths equal to or longer than 300 nm, ranging from the ultraviolet region to the visible light region, instead of that formed of a visible light-cutting filter in prior art. Installing such a transmission window allows mounting an object to be irradiated above this transmission window to irradiate advantageously the object.
The ultraviolet source can be, particularly, formed in a flat plate. Through this constitution, ultraviolet rays are emitted from one surface of the ultraviolet source and so it is easy to prevent exposure of an unnecessary site to ultraviolet rays. Moreover, forming a portion of the outer surface of the fluorescent transilluminator with a member constructing an emission surface of the ultraviolet source allows arranging the object to be irradiated directly on the member to raise irradiation efficiency of the object.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings, which illustrate examples of the present invention.